Parasound Zdac

Parasound Zdac ($475)
From the relatively affordable NewClassic line to the high-end Halo range, Parasound is well known and respected for their amplifiers and pre-amps. But did you know they once made excellent digital products as well? In the mid 90's, their D/AC-1500, D/AC-1100HD, and D/AC-1600HD units were all highly regarded. The series culminated with the D/AC-2000 Ultra which was a joint venture between Parasound and chip maker UltraAnalog. That unit sold for $2000 (which is nearly $3000 in today's dollars) and, when paired with the matching belt-drive C/BD-2000 transport, was once mentioned in Stereophile as having "one of the purest midrange productions I've heard." Clearly Parasound was once an important player in the digital game.

Fast forward to the 21st century, and we really haven't seen much from Parasound in this area. The last releases were the NewClassic D200 and the Halo D3 universal disc players at $1600 and $4000 respectively. But those were discontinued in 2008 with no digital products launched to replace them. That is, until now. The Zdac ($475) is part of Parasound's Z-series of compact components which was recently updated to include a tuner, amplifier, preamp, CD player, and of course the Zdac. All components are matching in size---8.5 inches wide, 10 inches deep, 2 inches high. Getting a unit in black widens the faceplate by an inch courtesy of extended sides for rack mounting. My Zdac review sample in silver looks very fetching and personally I think Parasound made a mistake using the black model in their marketing materials. Perhaps I'm merely associating the black chassis with the Paraound NewClassic line while the silver looks exactly like the upscale Halo models. It's not that black looks bad but rather that silver looks so good, and the majority of home users won't be rack mounting anyway.

So why the delay? DACs are big business these days and everybody knows it. I posed this question to Parasound head-honcho Richard Schram, who essentially confirmed what I already suspected: Parasound was well aware of the demand. Their distributors and customers had been clamoring for a new DAC for years. The expectation for a new Parasound DAC involved a highly favorable price to performance ratio, and Mr. Schram and Co. didn't feel they had the in-house expertise to deliver the type of game changing digital product they envisioned. Loathe to become another licensee of an existing technology, Parasound waited for the right opportunity to come along.

That opportunity presented itself when, through a series of mutual friends in the biz, Richard Schram was introduced to Thomas Holm of Danish firm Holm Acoustics. This proved just the ticket---Parasound has highly developed skills in terms of analog design, but they admittedly aren't on the same level when it comes to digital. Enter Holm and their expertise, as seen in their $16K two-box CD1/DSPre1 combo. Parasound teamed with Holm for their new $4500 Halo CD 1 player and figured they could leverage this partnership for a stand-alone DAC as well. Refreshingly, the goal was an affordable design, bucking the recent trend of multi-thousand dollar models.

DESIGN
The Zdac is a compact but full featured unit with plenty of connectivity. Inputs include coaxial and optical SPDIF as well as asynchronous USB. Somewhat unusually for a DAC in this price range, the Zdac offers XLR outputs in addition to the typical RCA option. An integrated headphone amp appears on the front panel via 1/8" jack, with a dedicated volume knob controlling headphone volume but not line-out which is fixed at 2.1 Vrms for RCA and double that for XLR.

Internally, all incoming signals pass through through an AD1895 asynchronous sample rate converter from Analog Devices which reclocks to 105.46875 kHz. This data is then passed to the AD1853 for D/A conversion using 4x oversampling. The net result (when rounded up) is the 422kHz upsampling figure seen in Parasound's marketing literature. Upsampling versus oversampling is a complextopic which I won't bore you with other than to call the process a good thing when done properly.

The Zdac accepts 24-bit/192kHz signals through both SPDIF inputs by way of an AKM AK4113 receiver. USB signals are handled by a TI TAS1020B which is an older USB 1.1 part rather than USB 2.0 and thus necessarily limited to 24-bit/96kHz signals. With many new USB DACs boasting 24/192 capabilities and beyond, the Zdac might initially seem underwhelming. Not so fast... this isn't your run-of-the-mill design.

Some DAC makers use the TAS1020B with its stock adaptive mode firmware and call it a day. Others like Benchmark, Lavry, and Bel Canto, license code from CEntrance, which offers much higher performance. Holm Acoustics has enough in-house expertise to create their own firmware from scratch which is not something many companies are equipped to do. This avoids licensing fees which would surely push this sub-$500 DAC into a higher price bracket. It also allows for potentially higher performance. USB 1.1 means no drivers needed - just plug and play. According to Holm, it's also more reliable with longer cable runs.

Without this special firmware, the TAS1020B output causes the AD1895 sample rate converter to trigger its polyphase filter coefficient generator. Altering the coefficients generates uncertainty in the sample rate conversion accuracy on the digital data output of the AD1895, even though the output clock is dead-stable. So the end effect is akin to jitter on the analog output of the AD1853 DAC IC. The result: impaired sound quality. Parasound summed it up for me like so:

"However, the Zdac's USB performance is superior to other DACs which use the TAS1020B: Holm Acoustics found significant shortcomings in TI's internal software which result in greater jitter on its digital output.

Holm discovered undocumented parts of the TAS1020B and replaced TI's own software with proprietary software which greatly reduces jitter on the TAS1020B digital output. This is accomplished through numerical optimization of its phase locked loop (PLL), providing a superior basis for maximizing the synergy of the AD1895 and AD1853 to further reduce USB timing errors. This means the AD1895 + AD1853 duo needs to do less "work" in bringing down the jitter. To get the widest bandwidth from the AD1895 in Master mode (self-generating I2S from the master clock on the output) a 27MHz crystal is used. 27MHz is the highest master clock frequency allowed for the AD1895."

The result: worthwhile sonic improvement.

HEADPHONE READY
The integrated headphone section is based around a TI TPA6120A2 high current amplifier. This amp chip is found in all types of gear ranging from the $100 FiiO E9 to the $1000 Kao Audio UD2C. It can sound mediocre or excellent, which, in my experience, largely depends on power supply quality. In this case Parasound uses a nice linear supply with a relatively large toroidal transformer which means the headphone section certainly has potential. It has a few odd design choices though---1/8" jack instead of 1/4" means an adapter is necessary for most full-size headphones. And a 10 ohm output impedance means it won't be ideal for certain low impedance headphones, particularly in-ear monitors using multiple balanced armature drivers.

Great review as always. Let's get this all off our chests as it is clearly the big elephant in the room:

How does it compare with the Yulong D100, which is almost identical in terms of features, price, and even specs (D100 using an AD1955 which is a suggested alternative for the AD1853 on the analog devices website)?

It depends on what sound you are going for. The Zdac has the advantage when used as a USB DAC. In terms of amp section, the Zdac would be my choice with HE-400, and the Yulong (with its lower output impedance) would be superior with HD598.

enjoyable review and I was going through the specs on the ZDAC priduct page that you have provided a link for. According to this page the output impedance of the headphone amp is 40 ohms on the headphone out. So , is this page wrong or did you get your information from an inaccurate source? also the I second the above question about the yulong.

As for output impedance - the original run had a resistor on the headphone stage for a 40 ohm output impedance. I questioned this, as the TPA6120 datasheet recommends 10 ohms. Turns out it was an arbitrary decision made by the factory who assembles the devices. Parasound fixed it, so everything after the very first run should have the lower spec. They are still working on updating the website, manual, and marketing sheets to reflect the lower number.

I don't want to take complete credit for this, and maybe they would have changed it regardless, but I was the one who first pointed it out.

I think you should absolutely take the credit for this. This might also explain why Steve Guttenberg felt that the ZDAC was inferior to the emotiva XDA-2(output impedance- 0.1 ohms). He mentioned that the difference was more stark when using headphones and he used 32 ohm M-100 for his comparison. Perhaps he got the ZDAC with a 40 ohm output impedance. As you can see I would like to believe that there is a an objective reason for your listening differences.

If you ever get a chance to try the older D/AC-1XXX units be sure to try bypassing the MOSFET output buffer. It sounds much cleaner that way. I really can't figure out why the buffer is needed in the first place, all it does is emit a ton of heat and add a lot of even order distortion.